Sandwich Mode Research Articles

Nanobody-based strategy for rapid and accurate pathogen detection: A case of COVID-19 testing

Antibody pairs-based immunoassay platforms served as essential and effective tools in the field of pathogen detection. However, the cumbersome preparation and limited detection sensitivity of antibody pairs challenge in establishment of a highly sensitive detection platform. In this study, using COVID-19 testing as a case, we utilized readily accessible nanobodies as detection antibodies and further proposed an accurate design concept with a more scientific and efficient screening strategy to obtain ultrasensitive antibody pairs. We employed nanobodies capable of binding different antigenic epitopes of the nucleocapsid (NP) or receptor-binding domain (RBD) antigens sandwich as substitutes for monoclonal antibodies (mAbs) sandwich in fast detection formats and utilized time-resolved fluorescence (TRF) microspheres as the signal probe. Consequently, we developed a multi-epitope nanobody sandwich-based fluorescence lateral flow immunoassay (FLFA) strip. Our results suggest that the NP antigen had a detection limit of 12.01pg/mL, while the RBD antigen had a limit of 6.51 pg/mL using our FLFA strip. Based on double mAb sandwiches, the values presented herein demonstrated 4 to 32-fold enhancements in sensitivity, and 32 to 256-fold enhancements compared to commercially available antigen lateral flow assay kits. Furthermore, we demonstrated the excellent characteristics of the proposed test strip, including its specificity, stability, accuracy, and repeatability, which underscores its the prospective utility. Indeed, these findings indicate that our established screening strategy along with the multi-epitope nanobody sandwich mode provides an optimized strategy in the field of pathogen detection.

Perceived Effect of COVID-19 on the Academic Performance and Satisfaction Level of Online Teaching of Sandwich Students

The study examined the perceived effect of COVID-19 on academic performance and the satisfaction level of online teaching of sandwich students on the OLA university campus. The study was a descriptive survey design with a quantitative approach. The accessible population was made up of 150 students. Through a multi-stage sampling approach, a sample size of 109 students was chosen for the study and determined using Miller and Brewer's (2003) sample size mathematical model. Data was collected using an adapted questionnaire with an r = .727. Data on respondents' demographic characteristics, as well as data to answer the four research questions, were analysed using descriptive statistics (frequencies, percentages, means, and standard deviations) and inferential statistics (Pearson Product Moment correlation, r). The study found a negative influence of the COVID-19 pandemic on students’ academic performance who study through the sandwich mode of learning. The study found that there is a high satisfaction level of online teaching among sandwich students. However, they are faced with problems of poor internet connection and the inability to purchase internet data/bundle for online learning. Ultimately, it was discovered that the degree of pleasure with online instruction and the effect of COVID-19 on academic achievement are not significantly correlated. The Ministry of Education, the universities, and all other relevant stakeholders were advised to provide online teaching apps. Also, they should provide professional training for online teaching applications and devices, Wi-Fi facilities, affordable internet packages, and virtual resources in light of the findings.

Iodinated organic molecule as tag for inductively coupled Plasma-mass spectrometry aptamer assays

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) aptamer-based assays using metallic nanostructures or chelates as exogenous tags have gained growing attention in the last decade. We describe here a proof-of-concept study based on the exploitation of a simple organic molecule as a tag, i.e.l-thyroxine carrying four iodine atoms detectable by ICP-MS. A solid-phase assay involving the structure-switching format was deployed for the detection of the small molecule l-tyrosinamide as model target. The overall design involved (i) a reporter agent consisting of a DNA aptamer incorporating a single l-thyroxine label at its end and (ii) a capture agent, which is a partially complementary strand, immobilized on a microplate. Limit of detection in the nanomolar range was reported. The present labeling approach was further developed for the detection of a model protein (α-thrombin), using a sandwich mode, and proved effective in a biological matrix. We believe that the l-thyroxine tagging method could become a simple and robust alternative to commonly used labeling methods for ICP-MS aptamer-based assays.

NIR II light response-based PDA/AuPt@CuS composites: Simultaneous readout of temperature and pressure sensing strategy for portable detection of pathogenic bacteria

In this study, we developed a simultaneous readout of pressure and temperature dual-signals platform based on the second near-infrared (NIR II) light response-based polydopamine (PDA)-functionalized-AuPt nanoparticles (NPs)@CuS nanosheets (PDA/AuPt@CuS NS) composite. Due to the excellent NIR photothermal performance of PDA/AuPt@CuS NS, it contribute to the decomposition of H2O2 and NH4HCO3 to generate gases (including O2, CO2, and NH3) can be promoted, which can amplify the pressure signals in a sealed container. A sandwich mode is formed between Fe3O4 NPs and PDA/AuPt@CuS NS based on the dual-aptamer when target pathogenic bacteria is present. And, it is possible to convert the molecular recognition signals between the dual-aptamers into amplified pressures and temperatures, which can be read out by a portable pressure meter and smartphones simultaneously. It may offer the possibility for quantitative POCT analysis of Pathogenic Bacteria. Moreover, because of the high photothermal efficiency of this method, the developed dual-mode method can achieve that following the detection of bacteria and killing them immediately. As a result, secondary contamination is eliminated and bacterial transmission is avoided. The developed dual-signal sensing platform is also inexpensive, simple to operate and rapidly, indicating that it can be used for food safety analysis, clinical applications, and environmental monitoring.

Discriminant Analysis of Gentiana Headspace Gas Chromatography – Mass Spectrometry Extract Data from In Vitro Cultures

Abstract A set of Gentiana L. species was successfully grown in vitro under the same conditions, and 72 samples from various cultures of these species (root, shoot, cotyledon callus, hypocotyl callus, and root callus) were obtained. The investigated species were G. affinis, G. andrewsii, G. bhutanica, G. burseri, G. cachemirica, G. capitata, G. crassicaulis, G. dahurica, G. decumbens, G. freyniana, G. frigida, G. gelida, G. grossheimii, G. kurroo, G. macrophylla, G. paradoxa, G. robusta, G. scabra, G. septemfida, G. siphonantha, and G. tianschanica. The obtained samples were extracted with a methanol-acetone-water (3:1:1) mixture, evaporated to dryness, and subjected to thin layer chromatography (TLC) on silica gel in sandwich mode with ethyl acetate-methanol-water (8:2:2) as the mobile phase. The resulting dry extracts were subjected to gas chromatography – mass spectrometry (GC-MS) fingerprinting of the headspace volatile fraction. Total ion count and average mass spectrum vectors were collected as two blocks and scaled independently to form a complex dataset. The major direction separating root or shoot samples from callus samples was found not to be fully associated with the highest variance as this information was placed in the first and fourth principal components of the principal component analysis (PCA). Therefore, linear discriminant analysis was performed on the first four (only the informative) components to reveal features responsible for the separation of culture types in the multivariate space.

A Monoclonal Antibody-Based Immunochromatographic Test Strip and Its Application in the Rapid Detection of Cucumber Green Mottle Mosaic Virus

Two specific monoclonal antibodies (mAbs) were screened, and an immunochromatographic strip (ICS) test for rapid and specific detection of cucumber green mottle mosaic virus (CGMMV) was developed. The coat protein of CGMMV was heterologously expressed as an immunogen, and specific capture mAb 2C9 and the detection mAb 4D4 were screened by an uncompetitive immunoassay. The test and control lines on the nitrocellulose membrane were coated with the purified 2C9 and a goat anti-mouse IgG, respectively, and a nanogold probe combined with 4D4 was applied to the conjugate pad. Using these mAbs, a rapid and sensitive ICS was developed. Within the sandwich mode of 2C9-CGMMV-4D4, the test line showed a corresponding positive relationship with CGMMV in infected samples. The ICS test had a detection limit of 1:5000 (w/v) for CGMMV in samples and was specific for CGMMV, with no observed cross-reaction with TMV or CMV.

Au@Ag-labeled SERS lateral flow assay for highly sensitive detection of allergens in milk

Casein and α-lactalbumin (α-LA) are the main allergens in cow's milk, which can affect the skin, respiratory system, and gastrointestinal tract, even cause anaphylactic shock. Developing a rapid and sensitive detection method of casein and α-LA is still pursued. Herein, a surface-enhanced Raman scattering based lateral flow assay (SERS-LFA) method for rapid and highly sensitive detection of milk allergens in food was established for effectively preventing allergic symptoms. Gold@silver nanoparticles (Au@Ag NPs) were synthesized as SERS active substrate to prepare the antibody-modified SERS Probe and SERS-LFA strips toward casein and α-LA were assembled according to the sandwich mode. The detection results were calculated according to colorimetric and Raman signal. The introduction of SRES signal significantly increased the sensitivity of detection with the limit of detection (LOD) of 0.19 ng/mL and 1.74 pg/mL, and exhibited an excellent linear relationship within the range of 0.55–791.50 ng/mL and 0.1 pg/mL–100.0 ng/mL for casein and α-LA, respectively. Furthermore, SERS-LFA strips was highly specific with the recovery rates for corresponding 80.36 %–105.12 % and 85.73 %–118.22 % for casein and α-LA, respectively. Therefore, the SERS-LFA could be in great potential to develop a unique allergen detection method.

Model of the SARS-CoV-2 Virus for Development of a DNA-Modified, Surface-Enhanced Raman Spectroscopy Sensor with a Novel Hybrid Plasmonic Platform in Sandwich Mode.

The recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has posed a great challenge for the development of ultra-fast methods for virus identification based on sensor principles. We created a structure modeling surface and size of the SARS-CoV-2 virus and used it in comparison with the standard antigen SARS-CoV-2—the receptor-binding domain (RBD) of the S-protein of the envelope of the SARS-CoV-2 virus from the Wuhan strain—for the development of detection of coronaviruses using a DNA-modified, surface-enhanced Raman scattering (SERS)-based aptasensor in sandwich mode: a primary aptamer attached to the plasmonic surface—RBD-covered Ag nanoparticle—the Cy3-labeled secondary aptamer. Fabricated novel hybrid plasmonic structures based on “Ag mirror-SiO2-nanostructured Ag” demonstrate sensitivity for the detection of investigated analytes due to the combination of localized surface plasmons in nanostructured silver surface and the gap surface plasmons in a thin dielectric layer of SiO2 between silver layers. A specific SERS signal has been obtained from SERS-active compounds with RBD-specific DNA aptamers that selectively bind to the S protein of synthetic virion (dissociation constants of DNA-aptamer complexes with protein in the range of 10 nM). The purpose of the study is to systematically analyze the combination of components in an aptamer-based sandwich system. A developed virus size simulating silver particles adsorbed on an aptamer-coated sensor provided a signal different from free RBD. The data obtained are consistent with the theory of signal amplification depending on the distance of the active compound from the amplifying surface and the nature of such a compound. The ability to detect the target virus due to specific interaction with such DNA is quantitatively controlled by the degree of the quenching SERS signal from the labeled compound. Developed indicator sandwich-type systems demonstrate high stability. Such a platform does not require special permissions to work with viruses. Therefore, our approach creates the promising basis for fostering the practical application of ultra-fast, amplification-free methods for detecting coronaviruses based on SARS-CoV-2.

Disrupted leptin-fatty acid biosynthesis is an early manifestation of metabolic abnormalities in schizophrenia.

BACKGROUNDInsulin resistance (IR) and impaired energy expenditure (IEE) are irreparable metabolic comorbidities in schizophrenia. Although mechanism(s) underlying IR and IEE remains unclear, leptin and fatty acid signaling, which has profound influence on insulin secretion/sensitivity, glucose metabolism and energy expenditure, could be disrupted. However, no association of plasma leptin with erythrocyte membrane fatty acids, body mass index (BMI), and psychotic symptoms in the same cohort of untreated patients with first-episode psychosis (FEP) or medicated patients with chronic schizophrenia (CSZ) is presented before. These studies are crucial for deciphering the role of leptin and fatty acids in the development of IR and IEE in schizophrenia.AIMTo determine the association between plasma leptin, erythrocyte membrane fatty acids, particularly, saturated fatty acids (SFAs), BMI and psychotic symptoms in patients with FEP and CSZ.METHODSIn this study, twenty-two drug naive patients with FEP, twenty-one CSZ patients treated with atypical antipsychotic drugs, and fourteen healthy control (CNT) subjects were analyzed. Plasma leptin was measured using sandwich mode enzyme-linked immunosorbent assay. Erythrocyte membrane SFAs were measured using ultrathin capillary gas chromatography. BMI was calculated by using the formula: weight (kg)/height (m2). Psychiatric symptoms were evaluated at baseline using brief psychiatric rating scale (BPRS), and positive and negative syndrome scale (PANSS). The total BPRS scores, positive and negative symptom scores (PANSS-PSS and PANSS-NSS, respectively) were recorded. Pearson correlation coefficient (r) analyses were performed to find the nature and strength of association between plasma leptin, PANSS scores, BMI and SFAs, particularly, palmitic acid (PA). RESULTSIn patients with FEP, plasma leptin not BMI was significantly lower (P = 0.034), whereas, erythrocyte membrane SFAs were significantly higher (P < 0.005) compared to the CNT subjects. Further, plasma leptin showed negative correlation with erythrocyte membrane SFAs-PA (r = −0.4972, P = 0.001), PANSS-PSS (r = −0.4034, P = 0.028), and PANSS-NSS (r = −0.3487, P = 0.048). However, erythrocyte membrane SFAs-PA showed positive correlation with PANSS-PSS (r = 0.5844, P = 0.0034) and PANSS-NSS (r = 0.5380, P = 0.008). In CSZ patients, plasma leptin, BMI, and erythrocyte membrane SFAs, all were significantly higher (P < 0.05) compared to the CNT subjects. Plasma leptin showed positive correlation with BMI (r = 0.312, P = 0.032) but not with PANSS scores or erythrocyte membrane SFAs-PA. However, erythrocyte membrane SFAs-PA showed positive correlation with PANSS-NSS only (r = 0.4729, P = 0.031). Similar changes in the plasma leptin and erythrocyte membrane SFAs have also been reported in individuals at ultra-high risk of developing psychosis; therefore, the above findings suggest that leptin-fatty acid biosynthesis could be disrupted before the onset of psychosis in schizophrenia.CONCLUSIONDisrupted leptin-fatty acid biosynthesis/signaling could be an early manifestation of metabolic comorbidities in schizophrenia. Large-scale studies are warranted to validate the above findings.

Helix Induction and Inversion of Polymeric Foldamer Regulated by the Single Enantiomers.

Generally, a single enantiomer can induce a foldamer into a preferred-handed helix, while another condition is required for the helical inversion. Herein, it is found that the helix induction and subsequent inversion of poly(m-phenylene diethynylene)-based foldamer bearing aza-18-crown-6 pendants (Poly-1) can be realized by increasing the concentration of sterically hindered l-amino acid perchlorate salts. When the amount of chiral enantiomers is small, one enantiomer tends to complex with two non-adjacent aza-18-crown-6 rings via three N+ H···O hydrogen bonds in a sandwich mode. Notably, the transition dipole moment is perpendicular to the aza-18-crown-6 ring, so that the induced helical chirality in Poly-1 backbone is opposite to the chirality of enantiomers. When the amount of chiral enantiomers is large enough, each aza-18-crown-6 is occupied by one enantiomer, which causes the transition dipole moment in a parallel direction to aza-18-crown-6 ring. In this case, the increased steric hindrance can facilitate the inversion of screw sense of Poly-1 backbone, which is directed by chiral center of enantiomers. As a result, a helix inversion has been achieved successfully. This work not only provides a novel strategy for regulating the two-stage folded helical conformations by the single enantiomers, but opens a window to develop chiral recognition materials.

Green fluorescent protein-fused bacteriophage cellular wall-binding domain as broad-spectrum signal probe for fluorimetry of methicillin-resistant Staphylococcus aureus strains

As a “superbug”, methicillin-resistant Staphylococcus aureus (MRSA) has long been one of the most ubiquitous drug-resistant bacteria inducing numerous nosocomial infections. To achieve effective diagnosis and following treatment decision of infectious diseases induced by MRSA, it is highly desired to establish rapid analysis and antibiotic susceptibility test methods for this pathogen. In this study, we successfully expressed a bifunctional protein by fusing green fluorescent protein and cellular wall-binding domain of bacteriophage P108. The bifunctional protein can be employed as a signal probe for broad-spectrum fluorimetry of MRSA strains because it can both bind with the target pathogen and emit intensive fluorescence. By using it as the signal probe and porcine IgG as the capture agent, MRSA can be analyzed within a dynamic range of 1.0 × 103–2.0 × 107 CFU mL−1 with a sandwich mode. The fluorimetry was also applied to test antibiotic susceptibility of this pathogen to five antibiotics, and all results are conformable with those obtained with a standard micro broth dilution method. The above results demonstrate the attractive perspective of the bifunctional protein for rapid diagnosis and effective medication of infectious diseases induced by MRSA.

Nanofiltration process in desalination phenomenon: Langevin dynamic model

The seawater desalination phenomenon can be carried out using different filtration processes such as reverse osmosis (RO), nanofiltration (NF)…etc. The presented work in this paper aims to address the modelling and simulation investigation of the desalination process of a fluid (water) by using a porous media doped with nanoparticles. The used materials contains two porous zones placed on sandwich mode. After a first filtration in the first zone, the fluid undergoes second nanofiltration by nanoparticles, which modulate its viscosity and friction coefficient. Our calculations are modelled by Langevin Dynamics based on the competition between stochastic and dissipation processes. The results show that desalination rate is more efficient with the presence of nanoparticles, and increases as power law with the ratio between the viscosity of salty fluid and pure one. Moreover, the used of nanoparticles with low concentration accelerate the desalination process and ameliorate its rate value.

Precise recognition of Zn(II) ions by a finely designed pair of α-NiS and β-NiS nanostructures: A sandwich mode recognition approach

We for the first time proposed a sandwich mode recognition approach for heavy metal ions based on the solubility product principle, i.e., a metal sulfide with a high solubility product is paired with a metal sulfide with a low solubility product to selectively identify a target heavy metal ion with an intermediate solubility product. In this work, a pair of α-NiS and β-NiS nanostructures with the same composition but different solubility product constants were synthesized, and the relationship of solubility product constants among α-NiS, β-NiS and ZnS is α-NiS < ZnS < β-NiS, conferring very different adsorption properties of α-NiS and β-NiS for Zn(II). The Zn(II) adsorption percentage of α-NiS hollow sphere is 99.5%, while that of β-NiS hollow sphere is only 14.5%. Using this finely designed pair of α-NiS and β-NiS, precise recognition of Zn(II) in mixed ions was realized, perfectly verifying the feasibility of the novel recognition protocol. This recognition method is simple and designable, and may be used for precise identification and rapid enrichment of targeted single or multiple heavy metal ions.

Engineering a superinsulating wall with a beneficial thermal nonuniformity factor to improve building energy efficiency

To increase the energy efficiency of buildings and lower carbon emissions, heat losses through exterior walls could be considerably decreased by using high-performance thermal insulation materials with superlow thermal conductivities or superhigh heat capacities. A superinsulating layer would result in a highly nonuniform distribution of thermal resistance and capacitance within the exterior wall. An interesting problem concerns how to engineer the nonuniform thermal distribution for given total resistances and capacitances to improve energy efficiency. This paper proposes using a thermal nonuniformity factor to quantitatively characterize the nonuniform distribution of thermal resistance and capacitance in an exterior wall built with superthermal aerogel insulating panels and given total resistance and capacitance values. Various thermal nonuniformity factors for several insulation modes were investigated by calculating the relevant transmission loads through the walls. The effect of the thermal nonuniformity factor on the wall transmission load was explored to improve the energy efficiency of a building. The results indicated that the wall heat flux could be greatly decreased by engineering walls with a high nonuniformity factor. For instance, engineering a wall in a sandwich mode with thermal nonuniformity factor of 0.97 could decrease the wall heat flux by ∼35% compared to a uniform wall. These findings on engineering walls based on thermal nonuniformity factors to decrease the wall heat flux could be a useful reference for superinsulated buildings and for further improving thermal insulating performance and building energy efficiency.

Nonnegative principal component analysis in thin layer fingerprint screening: A case of Gentiana extracts from in vitro cultures

Twenty-one species of Gentiana L. were successfully grown in vitro in the same conditions and 72 samples of various cultures of these species (root, shoots, cotyledon callus, hypocotyl callus, and root callus) were obtained. The investigated species were as follows: G. affinis, G. andrewsii, G. bhutanica, G. burseri, G. cachemirica, G. capitata, G. crassicaulis, G. dahurica, G. decumbens, G. freyniana, G. frigida, G. gelida, G. grossheimii, G. kurroo, G. macrophylla, G. paradoxa, G. robusta, G. scabra, G. septemfida, G. siphonantha, and G. tianschanica. The obtained samples were extracted with methanol–acetone–water (3:1:1) mixture, evaporated to dryness, and subjected to TLC on silica gel with mobile phase ethyl acetate–methanol–water (8:2:2) in sandwich mode. Data fusion of two densitometric modes: extinction at 254 nm and fluorescence at 312 nm (emission above 370 nm) were used as a fingerprint of each sample. Densitograms were denoised, subjected to baseline removal, warped, and analyzed with principal component analysis (PCA), hierarchical cluster analysis and—the novel proposal—nonnegative PCA. This allowed to split negatively intercorrelated fingerprint features to subsequent principal components (PCs), which increases the number of PCs required to see the same information, but these PCs are much more informative.

The Sandwich Mode for Vertical Shear Instability in Protoplanetary Disks

Abstract Turbulence has a profound impact on the evolution of gas and dust in protoplanetary disks (PPDs), from driving the collisions and the diffusion of dust grains, to the concentration of pebbles in giant vortices, thus, facilitating planetesimal formation. The vertical shear instability (VSI) is a hydrodynamic mechanism, operating in PPDs if the local rate of thermal relaxation is high enough. Previous studies of the VSI have, however, relied on the assumption of constant cooling rates, or neglected the finite coupling time between the gas particles and the dust grains. Here, we present the results of hydrodynamic simulations of PPDs with the PLUTO code that include a more realistic thermal relaxation prescription, which enables us to study the VSI in the optically thick and optically thin parts of the disk under consideration of the thermal dust-gas coupling. We show the VSI to cause turbulence even in the optically thick inner regions of PPDs in our two- and three-dimensional simulations. The collisional decoupling of dust and gas particles in the upper atmosphere and the correspondingly inefficient thermal relaxation rates lead to the damping of the VSI turbulence. Long-lived anticyclonic vortices form in our three-dimensional simulation. These structures emerge from the turbulence in the VSI-active layer, persist over hundreds of orbits and extend vertically over the whole extent of the turbulent region. We conclude that the VSI leads to turbulence and the formation of long-lived dust traps within ±3 pressure scale heights distance from the disk midplane.

Diversity of East China Summer Rainfall Change in Post-El Niño Summers

East China has experienced positive precipitation anomalies in post-El Niño summers, mainly in the Yangtze-Huaihe River Valley. This kind of monsoonal rainfall change induced by El Niño, however, is not always the same due to El Niño diversity and mean state change. Here, we use cluster analysis on the post-El Niño (PE) East China summer precipitation anomalies to identify the diversity of this El Niño-induced monsoon change. The result shows that PE East China summer rainfall anomalies mainly display three different modes for all selected 20 El Niño events from 1957 to 2016. Cluster 1 shows the middle and lower reaches of the Yangtze River demonstrate strong wet anomalies, while South and North China are dominated by dry anomalies, similar to a sandwich mode. Cluster 2 is distinguished by dry anomalies over South China and wet anomalies over North China, exhibiting a dipole mode. Compared with Cluster 1, the change caused by Cluster 3 is different, showing negative anomalies over the Yangtze-Huaihe River Valley. The three clusters are correlated with successive events of El Niño, a quick transfer to a strong La Niña and a quick transfer to a weak La Niña respectively. The associated anomalous anticyclone (AAC) focuses on (120°E, 20°N) in Cluster 1, which expands southward for Cluster 2 and moves eastward for Cluster 3. The feedback of AAC-sea surface temperature (SST) mainly works for supporting the AAC in Cluster 1, but it is weak for Cluster 2; the strong easterly anomalies related to La Niña contribute to the AAC location change for Cluster 2. Both AAC-SST feedback and easterly anomalies support the AAC of Cluster 3. The CMIP5 output can capture these diverse responses in circulation except that their simulated AAC for Cluster 1 is significant to the east of the observed.

Black-box approach for software testing based on fat-property

After a useful and summarized procedure of software testing is put forward based software engineering view, this paper proposed a definition of fat-property according to software testing activity in product quality monitoring software. Based on fat-property, black-box testing approach is deeply investigated. In unit testing, equivalence partitioning should include two aspects: data inputting type and function operating type. And a key point of black-box testing is design of boundary/sub- boundary testing case for data inputting type. In integration testing, Sandwich mode should be applied to improve coverage. In validation testing, keynote function and non- keynote function may be tested respectively to accelerate speed of testing and assure coverage of function. System testing based on black-box according to actual usage of software product is very important, and it will determine the quality level of software product.

Electrochemical sandwich aptasensor for the carcinoembryonic antigen using graphene quantum dots, gold nanoparticles and nitrogen doped graphene modified electrode and exploiting the peroxidase-mimicking activity of a G-quadruplex DNAzyme.

A sandwich-type electrochemical aptasensor has been constructed and applied for sensitive and selective detection of the carcinoembryonic antigen (CEA). The surface of a glassy carbon electrode (GCE) was first modified with nitrogen-doped graphene and then gold nanoparticles and graphene quantum dots electrodeposited on it to obtain an architecture of type GQD/AuNP/NG/GCE. In the next step, the CEA-binding aptamer was immobilized on the modified GCE. Hemin intercalates in the amino-modified hemin aptamer to form a hemin-G-quadruplex (hemin-G4) DNAzyme. The amino modified CEA aptamer II is connected to hemin-G4 by glutaraldehyde (GA) as a linker to produce CEAaptamerII/GA/hemin-G4 (=ApII/GA/DNAzyme). Through a sandwich mode, the ApII/GA/DNAzyme bioconjugates are captured on the modified GCE. Subsequently, the hemin-G4 acts as peroxidase-mimicking DNAzyme and rapidly catalyzes the electroreduction of hydrogen peroxide. The quantitative determination of CEA was achieved by differential pulse voltammetry, best at a working potential of around -0.27V vs. Ag/AgCl. Under optimized conditions, the assay has a linear response in the 10.0fgmL-1 to 200.0ngmL-1 CEA concentration range and a lower detection limit of 3.2fgmL-1. Graphical abstract Schematic presentation of a sandwich-type electrochemical aptasensor based on nitrogen doped graphene (NG), gold nanoparticles (AuNPs) and graphene quantum dots (GQDs) modified glassy carbon electrode, and thehemin-G4 DNAzyme for femtomolar detection of thecarcinoembryonic antigen.

Wrinkle-Free, Sandwich, Electrospun PLGA/SF Nanofibrous Scaffold for Skin Tissue Engineering

Electrospinning is a technique for creating continuous nanofibrous networks that can architecturally be similar to the structure of extracellular matrix. In this work, a simple and semiautomatic electrostatic spinning system is designed, and a method of multilayer composite electrostatic spinning is adopted, which is called the hierarchical construction (sandwich mode). Then, a kind of PLGA/silk fibroin composite electrospinning nanofibrous scaffolds is proposed for the growth of skin cells in combination with the good characters of silk fibroin and PLGA. The SEM experiment of the silk fibroin/PLGA composite nanofibers indicated that the prepared nanofibers are smooth, uniform in size, and have good porosity. The wrinkled contrast test shows that this nanofiber scaffold remains flat in the culture medium as the original, and is basically not shrink. The water absorption experimental results show that the composite nanofiber scaffold has good hydrophilicity, and the increase in water absorption with time is not obvious. The cell culture experiment is also shown that the skin cells can proliterate on the scaffold.